Radio communication systems capable of transmitting and displaying channel identification information to confirm proper operation of a portable radio receiver on a system at an expected location are well known. One such system is described in U.S. Pat. No. 4,981,638 to Davis, entitled "Nationwide Display Pager with Location Readout."
In a system that covers a wide area through a plurality of transmitters, location information received by the portable radio receiver preferably is that location information transmitted by the one of the plurality of transmitters that is nearest the portable radio receiver. Unfortunately, time-variant shadowing and multipath effects present in the radio communication system can cause the nearest transmitter at times not to be dominant over more distant transmitters as the portable radio receiver moves about the system. As a result, the location information received by the portable radio receiver can sometimes be incorrect.
Such momentarily incorrect location information can cause improper operation of the portable radio receiver if the receiver is near a boundary between locations that are intended to control the portable radio receiver to function differently from one location to the next. For example, if the user is near a time zone boundary, and the location information is used to automatically reset a clock in the receiver to display the time of day according to the time zone in which the receiver is located, the clock can occasionally display the wrong time of day.
Thus, what is needed is a method and an apparatus for distinguishing location information that is transmitted from a nearby transmitter from that transmitted by more distant transmitters in the system, even in the presence of the aforementioned time-variant shadowing and multipath effects.